1. Field of the Invention
The present invention relates to a light receiving module.
2. Related Background Art
The conventional light receiving modules are generally classified into the following two types. The first type embraces light receiving modules containing a waveguide type semiconductor photodetector, and the second type embraces light receiving modules containing a surface receiving type semiconductor photodetector.
In the technical field of optical communications, there are demands for light receiving modules capable of operating at high speeds. For example, these light receiving modules are recently required to perform transmission at about 10 Gbps. However, according to the inventor""s technical knowledge, it is not easy to develop a structure of an optical communication module capable of providing electric signals from the light receiving element at the foregoing fast transmission rate while maintaining sufficient coupling efficiency between an optical fiber and the light receiving element even with variation in alignment between the optical fiber and the light receiving element in manufacturing process. Namely, there are needs for an optical communication module capable of processing electric signals including transmission information at about 10 Gbps while maintaining the optical coupling efficiency.
In the optical communication modules of the former type, an optical fiber and a waveguide semiconductor photodetector are arranged on a straight line. In this configuration, the propagation direction of optical signals coincides with the transmission direction of electric signals. An end face of the optical fiber is optically coupled with one end face of the waveguide semiconductor photodetector. In the former type, since the optical characteristics of the optical communication modules are sensitive to the alignment between the optical fiber and the waveguide light receiving element, it is necessary to carry out the positioning of the two members with high accuracy.
In the latter type, the end face of the optical fiber is optically coupled with a light-receiving surface of the surface receiving type semiconductor photodetector. In this type, however, one end of the optical fiber faces the light receiving surface of the surface receiving type semiconductor photodetector. On the other hand, generally, the light receiving element and an electron device are placed on a common plane so as to be connected with each other, such that the light receiving element is connected through bonding wires to the electron device. In this configuration, the traveling direction of optical signals does not coincide with the traveling direction of electric signals. According to the inventor""s technical experiences, it can be hardly said that this structure is applicable to the light receiving modules.
Without using the above configuration, there is another candidate for the structure as shown below. This light receiving module has a configuration in which the surface receiving type semiconductor photodetector is mounted on one side face of a submount of rectangular parallelepiped and an electron device is mounted on an upper surface of the submount. The two devices are connected to each other through an conductive layer extending from the upper surface to the side face of the submount. In this structure, the optical fiber, surface receiving semiconductor photodetector, and electron device are arranged in a line, but the structure is complicated.
Another known module is an light receiving module in which the surface receiving type semiconductor photodetector and the electron device are mounted on an upper surface of a submount and in which light from one end of the optical fiber is guided via a concave mirror to the light-receiving surface of the surface receiving type photodetector. In this structure, the optical fiber, surface receiving type semiconductor photodetector, and electron device are also arranged in a line. However, an additional optical component such as the concave mirror is required for the optical coupling between the optical fiber and the surface receiving type semiconductor photodetector.
In both configurations above, the structures of the light receiving modules are complex and require their tolerance to be close for the alignment between the optical fiber and the photodetector. This means that a plateau region in the coupling efficiency between the optical fiber and the photodetector, i.e. the range in which the optical coupling efficiency is substantially invariable with variation in their alignment, is small.
It is an object of the present invention to provide an light receiving module capable of achieving satisfactory coupling efficiency between the optical fiber and the semiconductor photodetector and capable of increasing data transmission rates.
One aspect of the present invention is a light receiving module. The light receiving module comprises a mounting member, an optical fiber, a semiconductor photodetector, a mount substrate, and a signal processing semiconductor element.
The mounting member has a pair of arm portions and a connecting portion. Each of the arm portions extends in a first direction. The connecting portion extends in a direction intersecting with the first direction to connect the pair of arm portions. The optical fiber has a first end and a second end. The semiconductor photodetector has a light incidence surface optically coupled to the first end of the optical fiber, and a light receiving element portion. The mounting substrate is arranged between the pair of arm portions of the mounting member and is mounted with the optical fiber and the semiconductor photodetector. The signal processing semiconductor element is placed on the mounting member and processes a signal from the semiconductor photodetector.
By the mounting substrate, the optical fiber is enabled to be optically coupled to the semiconductor photodetector. The mounting substrate is placed between the pair of arm portions of the mounting member. This arrangement permits the placement of the signal processing semiconductor element in the proximity of the semiconductor photodetector. This placement ensures the satisfactory optical coupling between the optical fiber and the semiconductor photodetector and permits reduction in the length of electrical connection between the semiconductor photodetector and the signal processing semiconductor element in the light receiving module.
The light receiving module may also be configured to further comprise a housing capable of accommodating the mounting substrate and the mounting member. The housing has a plurality of wall portions and terminals. The mounting member is placed so as to be located between the mounting substrate and the wall portions. The semiconductor photodetector is electrically connected to the terminals via a wiring member placed on the mount member. The wiring member on the mounting member enables the reduction of a connection path between the semiconductor photodetector and the terminals of the housing.
In the light receiving module, the semiconductor photodetector has an electrode surface on which electrode pads are provided, and the semiconductor signal processor has a pad surface on which electrode pads are provided. The pad surface and the electrode surface are arranged to be positioned relative to a reference surface within manufacturing positional variations. This arrangement of the pad surface and the electrode surface makes a reduction feasible in the wire length between the semiconductor photodetector and the signal processing semiconductor element.
The light receiving module may also be configured to further comprise a housing that accommodates the mounting member and the mounting substrate and contains therein a wiring surface having a wiring layer. In this light receiving module, the signal processing semiconductor element has a pad surface on which electrode pads are provided. The wiring surface and the pad surface are arranged so as to be positioned relative to a reference surface within a range of manufacturing positional deviation. This arrangement of the wiring surface and the pad surface allows the reduction of a connection path between the wiring layer on the wiring surface and the signal processing semiconductor element.
In the light receiving module, the pad surface, the wiring surface, and the mounting surface of the mounting member are arranged so as to be positioned relative to a reference surface within a range of manufacturing positional deviation. This arrangement of the mounting surface, the pad surface, and the wiring surface makes a reduction feasible in connection paths among the semiconductor photodetector, the wiring layer on the wiring surface, and the signal processing semiconductor element.
In the above-stated configurations of the light receiving module, the connection paths can be formed of bonding wires, for example.
The features of the present invention described below can be combined with the invention as described above. The features of the present invention described below can be combined in arbitrary combination with each other, which permits the module to obtain respective functions and advantages and those achieved by the combination.
In the light receiving module, the optical fiber, the semiconductor photodetector and the signal processing semiconductor element are arranged in turn in a predetermined direction. The semiconductor photodetector is placed to face on one side of the signal processing semiconductor element. This placement enables the reduction of the wire length between the semiconductor photodetector and the signal processing semiconductor element because an optical signal from the optical fiber is incident to the semiconductor photodetector and an electric signal from the semiconductor photodetector propagates to the signal processing semiconductor element.
The light receiving module may also be configured so that the mounting member has a depressed portion provided in a principal surface thereof and the signal processing semiconductor element is placed in the depressed portion. According to the depth of the depressed portion, the pad surface of the signal processing semiconductor element can be adjusted in height with the reference surface.
The light receiving module may also be configured so that the mounting member has a thermal conductivity larger than that of the mounting substrate. In this configuration, the signal processing semiconductor element and the semiconductor photodetector are separately mounted on the mounting member and substrate, respectively. It also makes it feasible to place the signal processing semiconductor element on the mounting member, which generates heat greater than the semiconductor photodetector does. This allows the heat, generated in the signal processing semiconductor element, to efficiently conduct to the outside of the light receiving module. This heat is not transferred directly to the photodetector and the optical fiber because the mounting member is separate from the mounting substrate.
The light receiving module may also be configured so that the mounting substrate comprises first, second and third regions arranged on a principal surface thereof in the first direction. The first region is provided with an optical fiber supporting portion extending in the first direction. The second region is provided with a positioning portion having an abutment face extending in a direction intersecting with the first direction. The third region is provided with a photodetector mounting portion on which the semiconductor photodetector is mounted, and the photodetector mounting portion has a reflective surface extending in a direction intersecting with the first direction and a light introducing path for introducing the light from the optical fiber to the reflective surface.
This mounting substrate enables the alignment of the optical fiber and the semiconductor photodetector with predetermined accuracy. Light from the optical fiber is reflected by the reflective surface provided on the mounting substrate and thereafter travels via the light incidence surface of the semiconductor photodetector to the light receiving element portion thereof.
In the light receiving module, the optical fiber supporting portion has first and second supporting surfaces for supporting the optical fiber, and the optical fiber is supported by the first and second support surfaces while the first end of the optical fiber abuts against the abutment face.
In the light receiving module, the light incidence surface of the semiconductor photodetector has a monolithic lens thereon, and the semiconductor photodetector can be placed such that the light incidence surface thereof faces the photodetector mounting portion of the mounting substrate.
Since the semiconductor photodetector is provided with the monolithic lens, the relative positional accuracy becomes satisfactory between the photodetector portion and the monolithic lens. Although the monolithic lens is provided between the optical fiber and the light receiving portion, there is no need for additional alignment for the monolithic lens. In the light receiving module, the monolithic lens can enhance the optical coupling between the optical fiber and the semiconductor photodetector.
The position of the light receiving portion is also associated with the position of the first end of the optical fiber by the mounting substrate. The light from the optical fiber is converged in the light receiving portion by the monolithic lens. This can decreases the area of the light detection required for ensuring a predetermined amount of light. The reduction of the area results in the decrease of the capacitance of the light receiving portion.
In the light receiving module, the light introducing path has its size sufficient to accommodate the monolithic lens. In this structure, when the semiconductor photodetector is placed on the photodetector mounting portion, the light introducing path can accommodate the monolithic lens that is projected on the light incidence surface.
The light receiving module may also be configured that the housing has an inlet through which the optical fiber extends in s direction of a predetermined axis. The mounting substrate has an optical fiber introducing portion through which the optical fiber from the inlet passes, and this optical fiber introducing portion is provided so as to extend in the predetermined direction from one edge thereof, facing the inlet portion of the housing, up to the optical fiber supporting portion. The optical fiber is introduced through the inlet into the housing, then passes the optical fiber introducing portion, and thereafter reaches the optical fiber supporting portion on the mounting substrate. If there is a positional mismatch between the optical fiber in the inlet and the optical fiber supporting portion of the mounting substrate, the optical fiber can be bent between the housing and the mounting substrate. The optical fiber introducing portion is provided between the inlet of the housing and the optical fiber supporting portion of the mounting substrate, and can be utilized so as to compensate for the positional mismatch of the optical fiber between the inlet and the optical fiber supporting portion.
The light receiving module may also be configured to further comprise a cover member having a cover surface for positioning the optical fiber. The optical fiber is positioned in the first region by the first and second support faces and the cover surface of the cover member.
The light receiving module may also be configured to further comprise a ferrule having a pair of end faces and holding the optical fiber. The second end of the optical fiber appears at one of the pair of end faces of the ferrule.
The light receiving module may also be configured to further comprise a housing which accommodates the mounting member and the mounting substrate. The housing has first to third wall portions and a wiring surface provided along the first to third wall portions. The first and second wall portions extend in the first direction and the third wall portion extends in a direction intersecting with the first direction. The wiring surface has a wiring layer thereon. One of the arm portions of the mounting member is placed between the first wall portion and the mounting substrate. The other of the arm portions is placed between the second wall portion and the mounting substrate. The connecting portion is located between the third wall portion and the mounting substrate.
In the light receiving module, the optical fiber introducing portion comprises first and second faces defining a recess extending in a direction of a predetermined axis and letting the optical fiber pass. The optical fiber introducing portion has a taper region in an end thereof connecting to the optical fiber supporting portion. The taper region comprises first and second taper faces placed between the first and second support faces of the optical fiber supporting portion and the first and second faces of the optical fiber introducing portion, respectively. The first and second taper faces make obtuse angles with respect to the first and second support faces.
The light receiving module may also be configured to further comprise an island mounted with the mount member and the mounting substrate, a plurality of lead terminals, and a ferrule having a pair of end faces and holding the optical fiber. The second end of the optical fiber appears at one of the pair of end faces of the ferrule.
The light receiving module may also be configured to further comprise a resin body for molding the mount member, the mounting substrate, the semiconductor photodetector, and the signal processing semiconductor element therein. The ferrule projects out of the molding resin body.
In the light receiving module, the plurality of lead terminals are arranged to face on each of the pair of arm portions and the connecting portion of the mounting member.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.